U.S. patent application number 12/325317 was filed with the patent office on 2009-06-04 for method and medical apparatus for measuring pulmonary artery blood flow.
Invention is credited to Gabor Kovacs, Horst Olschewski, Gert Reiter, Ursula Reiter, Rainer Kurt Rienmueller.
Application Number | 20090143667 12/325317 |
Document ID | / |
Family ID | 40620974 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090143667 |
Kind Code |
A1 |
Kovacs; Gabor ; et
al. |
June 4, 2009 |
METHOD AND MEDICAL APPARATUS FOR MEASURING PULMONARY ARTERY BLOOD
FLOW
Abstract
In a method and apparatus for examination and evaluation of a
human or animal body as regards a blood flow in a pulmonary artery
(PA), measurement data are recorded, from which at least a part of
the blood flow in the pulmonary artery (PA) is able to be
re-constructed at least two-dimensionally in a plane defined by a
longitudinal axis of the pulmonary artery (PA) and by an
anterior-posterior direction, including at least at several
diastolic points in time in the course of a heart cycle, after a
closure of the pulmonary valve. The measurement data are analyzed
as to how many of the at least several diastolic points in time in
the flow behavior of the blood flow of the pulmonary artery an
asymmetry in relation to the longitudinal axis of the pulmonary
artery in the anterior-posterior direction exists. A measure is
then determined that characterizes how long, after the closure of
the pulmonary valve in the flow behavior of the blood flow of the
pulmonary artery, the aforementioned asymmetry exists.
Inventors: |
Kovacs; Gabor; (Graz,
AT) ; Olschewski; Horst; (Graz, AT) ; Reiter;
Gert; (Graz, AT) ; Reiter; Ursula; (Graz,
AT) ; Rienmueller; Rainer Kurt; (Graz, AT) |
Correspondence
Address: |
SCHIFF HARDIN, LLP;PATENT DEPARTMENT
6600 SEARS TOWER
CHICAGO
IL
60606-6473
US
|
Family ID: |
40620974 |
Appl. No.: |
12/325317 |
Filed: |
December 1, 2008 |
Current U.S.
Class: |
600/410 ;
600/454; 600/504 |
Current CPC
Class: |
A61B 5/7207 20130101;
A61B 5/0263 20130101; A61B 5/7289 20130101; A61B 8/06 20130101;
A61B 5/021 20130101; A61B 5/055 20130101 |
Class at
Publication: |
600/410 ;
600/504; 600/454 |
International
Class: |
A61B 8/06 20060101
A61B008/06; A61B 5/026 20060101 A61B005/026; A61B 5/055 20060101
A61B005/055 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 2007 |
DE |
10 2007 057 553.1 |
Claims
1. A method for examination and evaluation of a human or animal
body in relation to a blood flow in a pulmonary artery (PA),
comprising the steps of: (a) recording measurement data, from which
at least a part of the blood flow n the pulmonary artery (PA) is
re-constructed at least two-dimensionally in a plane spanned by a
longitudinal axis of the pulmonary artery (PA) and by an
anterior-posterior direction, including a plurality of diastolic
points in time in the course of a heart cycle, after a closure of
the pulmonary valve (PV), (b) at least semi-automatically analyzing
the measurement data to identify at how many diastolic points,
among said plurality of diastolic points in time, an asymmetry
exists as to the longitudinal axis of the pulmonary artery (PA) in
the anterior-posterior direction; (c) at least semi-automatically
determining a measure that characterizes how long after the closure
of the pulmonary valve (PV) in the flow behavior of the blood flow
of the pulmonary artery said asymmetry exists; and (d) making said
measure available as an output.
2. The method as claimed in claim 1, comprising during the step of
recording the measurement data, recording the measurement data to
allow at least a part of the blood flow in the pulmonary artery
(PA) to be reconstructed three-dimensionally from the measurement
data.
3. The method as claimed in claim 1, comprising in the step of
recording the measurement data, recording the measurement data
distributed over the entire heart cycle, to allow the time gradient
of the at least one part of the blood flow to be determined over
the entire heart cycle from the recorded measurement data.
4. The method as claimed in claim 1, comprising in the step of
analyzing the measurement data, at least semi-automatically
examining the blood flow to establish at which said diastolic
points in time in the anterior third of the pulmonary artery a flow
in the movement direction of the pulmonary artery exists that is
greater than a flow in the posterior third of the pulmonary artery
(PA).
5. The method as claimed in claim 1, comprising in the step of
analyzing the measurement data, at least semi-automatically
examining the blood flow to establish at how many of the at least
several diastolic points in time a vortex exists which has a vortex
axis which is essentially transverse to the longitudinal axis of
the pulmonary artery (PA) and transverse to the anterior-posterior
direction.
6. The method as claimed in claim 1, comprising determining the
measure determining, for the at least several diastolic points in
time, the number of points at which the flow behavior of the blood
flow of the pulmonary artery (PA) at which asymmetry regarding the
longitudinal axis of the pulmonary artery (PA) exists in the
anterior-posterior direction and is related to the total number of
the at least several diastolic points in time.
7. The method as claimed in claim 1, comprising at least
semi-automatically determining a predicted value characterizing the
pulmonary blood pressure, from the measure via a stored
correlation, by a linear correlation or logarithmic
correlation.
8. The method as claimed in claim 1, comprising generating a signal
if the measure exceeds a threshold value.
9. The method as claimed in claim 1, comprising generating a
graphic presentation of the blood flow in the pulmonary artery
after recording the measurement data, and analyzing the measurement
data using the graphic presentation of the blood flow in the
pulmonary artery.
10. The method as claimed in claim 9, comprising generating the
graphic presentation of the blood flow using a vector field.
11. The method as claimed in claim 1, comprising recording the
measurement data in a magnetic resonance examination.
12. The method as claimed in claim 11, comprising recording the
measurement data being recorded with a flash (fast low angle shot)
sequence-based phase contrast measurement.
13. The method as claimed in claim 1, comprising recording the
measurement data with an ultrasound examination method.
14. A medical imaging apparatus comprising: a measurement unit that
interacts with a patient to obtain measurement data from the
patient, from which at least a part of the flood flow in the
pulmonary artery (PA); a computer that at least two-dimensionally
reconstructs said flood flow in the pulmonary artery from said
measurement data, in a plane defined by a longitudinal axis of the
pulmonary artery and by an interior-posterior direction, that
includes a plurality of diastolic points in time in the course of a
hard cycle, after a closure of the pulmonary valve (PV); and a
processor configured to at least semi-automatically analyze said
measurement data to identify how many diastolic points, among said
plurality of diastolic points in time, and asymmetry exists as to
the longitudinal axis of the pulmonary artery in the
interior-posterior direction, and to determine a measure that
characterizes how long after said closure of the pulmonary valve in
the flow behavior of the blood flow of the pulmonary artery said
asymmetry exists, and to make said measure available as an output
from said processor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns a method for examining a
human or animal body with regard to a blood flow in the pulmonary
artery. In addition the invention concerns a medical imaging
apparatus for implementing such a method. Such a method is
especially used in the examination of patients with a pulmonary
hypertension or with a suspected pulmonary hypertension or with a
pulmonary hypertension occurring when the body is under stress.
[0003] 2. Description of the Prior Art
[0004] Pulmonary hypertension (abbreviated "PH" below) is an
illness characterized by an increase in the pulmonary artery
pressure. Pulmonary arterial hypertension (abbreviated "PAH" below)
is a subgroup of PH. The definition of PAH has been established in
the usual guidelines. It relates to the mean pulmonary artery
pressure (mPAP) and not to the systolic pulmonary artery pressure
(sPAP) and to the exclusion of basic conditions such as serious
lung or left heart diseases. PAH exists if the mean pulmonary
artery pressure (mPAP) exceeds 25 mm Hg at rest or 30 mm Hg under
stress. By comparison, the normal pulmonary pressure at rest is
below 21 mm Hg. The prognosis of the PH is bad regardless of its
genesis, especially if the diagnosis is made late.
[0005] Overview articles and guidelines about pulmonary
hypertension can be found in the publications Galie N et al.,
"Guidelines on diagnosis and treatment of pulmonary arterial
hypertension", The Task Force on Diagnosis and Treatment of
Pulmonary Arterial Hypertension of the European Society of
Cardiology, Eur Heart J 2004; 25(24): 2243-2278 and Olschewski H et
al., "Diagnosis and therapy of chronic pulmonary hypertension"
Pneumologie 2006; 60(12): 749-771.
[0006] A right heart catheter examination (swan-neck catheter) is
currently seen as the "gold standard" method of examination for the
determination of pulmonary artery pressure and thereby for the
diagnosis of pulmonary hypertension. This examination is invasive
however and must be carried out by experienced personnel to obtain
reliable data and to keep the risks low. The costs of such an
examination are high.
[0007] The publications Chemia D et al. "Haemodynamic evaluation of
pulmonary hypertension" Eur Respir J 2002; 20: 1314-1331, Denton C
P et al. "Comparison of Doppler Echocardiography and Right Heart
Catheterization to Assess Pulmonary Hypertension in Systemic
Sclerosis" Br J Rheumatology 1997; 36: 239-243, Laaban J P et al.
"Estimation of Systolic Pulmonary Artery Pressure Using Doppler
Echocardiography in Patients with Chronic Obstructive Pulmonary
Disease" Chest 1989; 96: 1258-1262, and Hinderliter A L et al.
"Effects of Long-term Infusion of Prostacyclin (Epoprostenol) on
Echocardiographic Measures of Right Ventricular Structure and
Function in Primary Pulmonary Hypertension" Circulation 1997; 95:
1479-7486 deal with methods such as the color doppler
echocardiography method with which the systolic pulmonary artery
pressure (abbreviated below "sPAP") can be determined from the
maximum regurgitation velocity of a tricuspid insufficiency. This
method is currently used as a screening examination for
establishing pulmonary arterial hypertension. For patients with PAH
the sensitivity is around circa 90% and the specificity is around
67% to 75%. The accuracy of the estimation in a healthy control
population is however not known. In addition the practice of
computing the mPAP from the sPAP is not established.
[0008] Other alternative non-invasive methods are subordinate to
color doppler echocardiography.
[0009] A method is known from the publication Kitakabe A I et al.
"Noninvasive evaluation of pulmonary hypertension by a pulsed
Doppler technique" Circulation 1983; 68: 302-309 in which the
acceleration time of the blood stream is determined with the aid of
color doppler echocardiography and used as the correlate to the
logarithm of the mPAP.
[0010] A method is known from the publication Mousseaux E et al.
"Pulmonary arterial resistance; noninvasive measurement with
indexes of pulmonary flow estimated at velocity-encoded MR
imaging--preliminary experience" Radiology 1999; 21 2(3): 896-902
in which inter alia the maximum changes over time of the blood flow
is determined from one-dimensional magnetic resonance
phase-contrast flow measurements in the pulmonary artery as the
correlate to pulmonary vascular resistance.
[0011] Known from the publications Laffon E et al. "Noninvasive
assessment of pulmonary arterial hypertension by MR phasemapping
method" J Appl Physiol 2001; 90: 2197-2202, and Laffon E et al. "A
computed method for noninvasive MRI assessment of pulmonary
arterial hypertension" J Appl Physiol 2004; 96; 463-468 are methods
in which the pressure wave velocity and the maximum blood stream
velocity can be measured with the aid of one-dimensional
magnetic-resonance phase-contrast flow quantities in the pulmonary
artery and an optimum functional relationship to mPAP determined.
These types of results were not able however to be reliably
reproduced by other working groups.
[0012] In the publication Kondo C et al. "Pulmonary Flow
Quantification and Flow Profile Analysis with Velocity-encoded Cine
MR Imaging" Radiology 1992; 183: 751-758 the relationship is
demonstrated that patients with a PH exhibit a greater proportion
of retrograde blood flow in the pulmonary artery.
[0013] The publication Mohiaddin R H et al. "Visualization of flow
by vector analysis of multidirectional cine MR velocity mapping",
Journal of computer assisted tomography 1994, 18: 383-392 describes
how, in patients with pulmonary hypertension in the diastole, a
backwards-directed flow in the pulmonary artery is detectable.
[0014] All the publications cited represent small explorative
series. Most of the methods described therein have not been able to
establish themselves.
SUMMARY OF THE INVENTION
[0015] An object of the invention is to provide a method that
supports a user in examinations within the context of diagnosis of
pulmonary hypertension in a reliable manner and that can be
implemented substantially independently of the user. Furthermore it
is an object of the invention to specify a medical imaging
apparatus with which such a method can be implemented.
[0016] The method in accordance with the invention, for examination
an evaluation of a human or animal body in relation to a blood flow
in an pulmonary artery, includes the following steps:
[0017] (a) Recording measurement data from which at least a part of
the blood flow in the pulmonary artery is able to be reconstructed
at least two-dimensionally in a plane spanned by a longitudinal
axis of the pulmonary artery and by an anterior-posterior
direction, including at least at several diastolic times in the
course of a heart cycle, after a closure of the pulmonary
valve,
[0018] (b) Analysis of the measurement data in respect of at how
many of the at least several diastolic times in the flow behavior
of the blood flow of pulmonary artery an asymmetry as regards the
longitudinal axis of the pulmonary artery in the anterior-posterior
direction exits,
[0019] (c) Determining a measure that characterizes how long after
the closure of the pulmonary valve in the flow behavior of the
blood flow of the pulmonary artery asymmetry as regards the
longitudinal axis of the pulmonary artery in the anterior-posterior
direction exists; and
[0020] (d) Making the measure available as an output.
[0021] The basis of the method is that conclusions can be drawn
from a specific flow behavior of the blood flow in the pulmonary
artery about whether or not pulmonary hypertension is present in
the patient under examination. Changes in the blood flow can be
caused by pulmonary hypertension which are reflected in the
three-dimensional flow pattern in the pulmonary artery. In this
case it has been recognized that an asymmetry in the flow behavior
of the blood flow as regards the longitudinal axis of the pulmonary
artery can be used to obtain significantly more informative results
than with known methods, such as those described at the outset for
example.
[0022] More precisely it was recognized in this case that the
length of time for which a specific flow behavior exists in the
pulmonary artery can be correlated especially well with the
presence of a pulmonary arterial hypertension. The period in such
cases can be described with a measure which characterizes the
length of the period. In this case the interval which is the length
of time that a specific flow behavior obtains in the pulmonary
artery after the closure of the pulmonary valve, above all during
the diastole, is of especial significance. For example after
determination of the measure a signal is created if the measure
exceeds a specific threshold value. In this manner a user is made
aware of the possible existence of a pulmonary hypertension. In
particular the measure is determined by evaluating the number of
those times from the at least several diastolic time at which the
asymmetric flow behavior was present. The measure determined by the
method for examining the blood flow in the pulmonary artery can
give a user important information within the framework of diagnosis
of a PH. To this extent the method can support the diagnosis in
relation to a pulmonary hypertension.
[0023] The method can also be used with other medical diseases
which are associated with the risk of a PH. In this way patients
with heart disease (e.g. chronic left heart diseases, right heart
insufficiency, congenital, acquired and postoperative defects),
with chronic obstructive pulmonary diseases (COPD), with
thromboembolisms can be examined. In such cases the method can be
used for manifest diseases in each case as well as for diagnosis of
suspected disease and diagnosis to exclude disease.
[0024] In the described method above, all the individual steps--as
for example the step of recording of measurement data or the step
of analyzing measurement data and/or the step of determining the
measure--can be executed automatically or semi-automatically in
interaction with a user. In this way the method can be executed to
a large extent independently of a user. For example the measurement
data can be recorded with a magnetic resonance examination,
especially with a phase-contrast measurement. For example a flash
(fast low-angle shot)-based phase-contrast measurement can be used
as the magnetic resonance sequence. In this way the measurement
data obtained is far more constant and independent of a user who is
conducting the examination, compared for example to a conventional
color doppler echocardiography examination undertaken with an
ultrasound device. Although such an examination is in principle
also possible, it can be rendered more difficult for example by
anatomical changes or by peculiarities of the examination site such
as a lung overinflation for example. In principle all diagnostic
modalities which allow a two-dimensional and especially
three-dimensional presentation of blood flow fields can be employed
for data recording.
[0025] In addition the recording of the measurement data can be
undertaken without application of contrast media, which enhances
safety for a patient. Overall the method is fast, simple and
risk-free.
[0026] The evaluation of the measurement data itself and the
determination of the measure can be implemented fully automatically
in such cases or for example such that parts of the method steps
are undertaken in interaction with a user. For example a user can
identify particular areas in the pulmonary artery which have a
particular flow pattern, so that the further evaluation can be
carried out automatically on this basis.
[0027] This enables screening examinations to be implemented in a
simple manner providing a user with reliable intermediate results
with which a user can assess the existence of a pulmonary
hypertension as likely or less likely. The prognosis of pulmonary
hypertension, which is bad regardless of its genesis, especially if
the diagnosis is conducted late, can be improved In this way
without having to have recourse to invasive examination
methods.
[0028] The measurement data is recorded in such cases such that at
least a part of the blood flow in the pulmonary artery is able to
be reconstructed in the plane defined by the longitudinal axis of
the pulmonary artery and by the anterior-posterior direction. This
plane essentially corresponds to a sagittal plane or a
sagittal-oblique plane. The recording of the measurement data can
in such cases for example also be undertaken in transversal planes,
such that a reconstruction of the blood flow can subsequently be
undertaken in a sagittal or sagittal-oblique plane.
[0029] In an embodiment, during the step of recording the
measurement data the measurement data is recorded such that from
the measurement data at least one part of the blood flow in the
pulmonary artery is able to be reconstructed three-dimensionally.
In this way the detection of the asymmetry with regard to the
longitudinal axis of the pulmonary artery in the anterior-posterior
direction is possible more exactly and more quickly, since
three-dimensional data of the blood flow is available in order to
detect a specific flow behavior. The danger of overlooking a
specific flow behavior since a two-dimensional plane may possibly
not run exactly through the area with the characteristic flow
behavior of the blood flow is in this way significantly less.
[0030] In an embodiment, during the step of recording the
measurement data the measurement data is recorded distributed over
the entire heart cycle. This enables the time gradient of the at
least one part of the blood flow over the entire heart cycle to be
determined from the recorded measurement data. This means that in
addition to the at least several diastolic points in time, systolic
points in time are also included. The step of analyzing the
measurement data can In this way be executed more exactly since in
addition to the diastolic time range of the heart cycle, the
systolic range of the heart cycle is now also available.
[0031] Preferably during analysis of the measurement data the blood
flow in the pulmonary artery is examined to establish at how many
diastolic points in time there is a flow in the anterior third of
the pulmonary artery in direction of movement of the pulmonary
artery which is greater than a flow in the posterior third of the
pulmonary artery. In such cases flow differences between the
anterior third and the posterior third which lie below a threshold
value remain unconsidered. This can for example be implemented by
an algorithm for evaluation of smaller flows not being recorded and
only flows as from a certain size being taken into account. This
means that smaller flow differences, which also occur in the
electrophysiological case in the blood flow, are not taken into
consideration. Especially, if after closure of the pulmonary valve
a marked flow difference between the anterior third of the
pulmonary artery and the posterior third of the pulmonary artery is
present over a certain period of time, this indicates the presence
of a pulmonary hypertension.
[0032] In an advantageous embodiment, during the step of analyzing
the measurement data, the blood flow in the pulmonary artery is
examined to establish at how many of the at least several diastolic
points in time a vortex is present which has a vortex axis which
lies essentially transverse to the longitudinal axis of the
pulmonary artery and transverse to the anterior-posterior
direction. This type of vortex is an especially clear form of the
asymmetry in the flow behavior of the blood flow in the pulmonary
artery. In such cases, in an area which faces the anterior wall of
the pulmonary artery the vortex has a flow in the direction of
movement of the pulmonary artery, while the vortex in an area which
faces the posterior wall of the pulmonary artery has a flow against
the direction of movement of the pulmonary artery. In addition the
vortex has a first transverse component which is directed in the
posterior-anterior direction, as well as a second transverse
component which is directed in the anterior-posterior direction.
The first transverse component lies in this case closer to the
pulmonary valve than the second transverse component. It has
especially been established that the presence of such a vortex in
the blood flow of the pulmonary artery, especially at a diastolic
point in time, gives a clear indication of a pulmonary hypertension
under rest conditions. Usually this type of vortex already occurs
during the systolic phase. Its existence extends however also into
the diastolic phase if a pulmonary hypertension exists under rest
conditions.
[0033] However merely the presence of an asymmetrical flow along
the longitudinal axis of the pulmonary artery without vortex
formation can count as a clear indication that the patient to be
examined exhibits a stress-induced pulmonary hypertension.
[0034] The measure that characterizes the period of time at which a
specific flow behavior exists in the pulmonary artery--such as an
anterior-posterior asymmetry or a vortex--can be determined in a
simple manner by the number of times at which the specific flow
behavior exists in the blood flow of the pulmonary artery being
related by the overall number of the recorded times. As an
alternative to this for example the absolute number of the points
in time can be used as a measure at which the specific flow
behavior exists in the blood flow of the pulmonary artery. In
another variant for example the absolute period or the relative
period can be determined relative to the overall period of the
heart cycle during which the specific flow behavior exists, such as
for example the described anterior-posterior asymmetry in the flow
behavior of the pulmonary artery or the described vortex.
[0035] In a further advantageous embodiment variant a predicted
value can be determined with the use of the determined measure
which characterizes the pulmonary blood pressure. In this way the
method is developed into a method for examination of a human or
animal body in relation to a blood pressure. In particular a
prediction value for the average arterial pulmonary blood pressure
can be determined. This can be done for example using a correlation
held in a memory of a processing unit. Examinations have revealed
in such cases that the period during which the specific flow
behavior exists correlates well with a measured mean pulmonary
arterial blood pressure in a linear or logarithmic manner. The
method is sensitive, fast, simple and risk-free. It can be used
both as a screening method, for follow-ups as well as possibly as a
replacement for an invasive examination.
[0036] In an embodiment variant, after the step of recording the
measurement data, a graphic presentation of the blood flow in the
pulmonary artery is generated. The step of analyzing the
measurement data can then be undertaken with the aid of or on the
graphic representation of the blood flow in the pulmonary artery.
Graphic representations of the time-resolved flow fields can for
example visualize the blood flow with the aid of a vector field,
especially with the aid of a color-coded vector-field. Methods for
this are disclosed for example in the Publication by Reiter G et
al. "MR vector field measurement and visualization of normal and
pathological time-resolved three-dimensional cardiovascular blood
flow patterns" J Cardiovasc Magn Reson 2007; 9: 237-238. Such
methods can be implemented by software.
[0037] The inventive medical imaging apparatus has a processor unit
for control of the medical imaging apparatus and for evaluation of
recorded measurement data and is embodied for implanting the method
as described above, and all embodiments thereof. The processor unit
in this case can be implemented as a single processor unit or also
be divided up into one or more subunits, of which each subunit
assumes specific control and/or evaluation tasks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a schematic diagram of the blood flow in the
pulmonary artery which exhibits a characteristic, asymmetrical flow
behavior with regard to the anterior-posterior direction.
[0039] FIG. 2 is a schematic diagram of the blood flow which
exhibits a characteristic vortex for the existence of a pulmonary
hypertension.
[0040] FIG. 3 is a schematic overview of the characteristic
behavior of the blood flow for a healthy person, for a patient with
pulmonary hypertension and for a patient with stress-induced
pulmonary hypertension.
[0041] FIG. 4 is a correlation between the period of the presence
of a characteristic vortex field and a measured mean pulmonary
arterial blood pressure.
[0042] FIG. 5 is a schematic overview of method steps of an
embodiment of the inventive method.
[0043] FIG. 6 is a schematic overview of a medical imaging
apparatus, with which embodiments of the inventive method can be
executed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] FIG. 1 shows a schematic diagram of the blood flow in the
pulmonary artery PA at a diastolic point in time after closure of
the pulmonary valve PV with a characteristic asymmetrical flow
behavior. The asymmetry relates to a difference in the flow
behavior in the anterior-posterior direction in relation to the
longitudinal axis 11 of the pulmonary artery, RV identifies the
outflow tract in the right ventricle, the letters a and p the
anterior or the posterior direction respectively. The blood flow in
the pulmonary artery PA is consequently shown in an essentially
sagittal plane. It can clearly be seen that the blood flow in the
anterior third of the pulmonary artery PA is parallel to the
anterior wall 13 of the pulmonary artery PA. This blood flow is
considerably stronger than the blood flow in the posterior third of
the pulmonary artery PA. If such a flow behavior exists over a
certain period during the diastole after closure of the pulmonary
valve PV, this indicates that a patient to be examined exhibits at
least one stress-induced pulmonary hypertension.
[0045] FIG. 2 shows a schematic diagram of the blood flow in the
pulmonary artery PA in the same plane, with the blood flow this
time having a characteristic vortex 15, of which the vortex axis 17
points essentially perpendicular to the longitudinal axis of the
pulmonary artery PA and essentially perpendicular to the
anterior-posterior direction. In the anterior area of the pulmonary
artery PA the vortex 15 features components in the flow direction
of the pulmonary artery PA, while in the posterior area of the
pulmonary artery PA the vortex 15 features components which point
in the opposite direction of flow of the pulmonary artery PA. In
addition the vortex 15 exhibits a clearly marked first transverse
component from anterior to posterior and a clearly marked second
transverse component from posterior to anterior. The second
transverse component in this case lies closer to the pulmonary
valve PV than the first transverse component. If this type of
vortex 15 is present for a certain period during the diastole after
closure of the pulmonary valve PV, this indicates that the patient
under examination has a pulmonary hypertension under rest
conditions. Usually such a vortex already occurs in the
systole.
[0046] The evidence of such a correlation has been investigated in
a study. In this study 38 patients with suspected pulmonary
hypertension or with an already proven pulmonary hypertension were
investigated. With all patients both a right heart catheterization
and also a magnetic resonance phase-contrast examination of the
pulmonary artery was carried out. Of the 38 patients, 22 patients
exhibited a pulmonary hypertension under rest conditions and 13
patients merely exhibited a stress-induced pulmonary hypertension.
Three patients exhibited a normal mPaP under rest conditions and
under stress. Ten healthy comparison persons without a previous
history with a cardiovascular or pulmonary disease were likewise
subjected to an MR phase-contrast examination of the pulmonary
artery. Normal left and right ventricular functional parameters
were checked on the basis of a conventionally EKG triggered cine MR
phase-contrast imaging.
[0047] Based on the right heart catheter examination the 38
patients with a suspected or an already verified pulmonary
hypertension can be classified into different groups, namely into
patients without a pulmonary hypertension, into patients with a
pulmonary hypertension under rest conditions as well as into
patients with a stress-induced pulmonary hypertension.
[0048] The magnetic resonance imaging was undertaken EKG-triggered
on a 1.5 Tesla appliance (MAGNETOM Sonata, Siemens) with a
6-channel heart coil. The examination was carried out in a supine
position of the subject or patient.
[0049] In order to record velocity field measurement data the
pulmonary artery was sampled seamlessly in the orientation of the
right ventricular outflow tract by two-dimensional, retrospectively
EKG-triggered, flashed-based (flash=fast low angle shot)
phase-contrast sequences. The right ventricular outflow tract was
covered with the two-dimensional phase-contrast measurements with
velocity encoding in all spatial directions (1 to 4 measurements,
duration appr. 1 to 5 minutes).
[0050] Velocity data was able to be recorded with a simple
four-point velocity encoding scheme. For presentation the velocity
encoding was set to 90 cm/s in all directions and adapted if
necessary if aliasing was observed in the main stem of the
pulmonary artery.
[0051] Further parameters which were employed in the protocol used,
are for example a field-of-view of 234-246.times.340 mm.sup.2, an
image matrix of 96-114.times.192 pixels (interpolated to
192-228.times.384), a flip angle of 15.degree., 89 ms repetition
time, reconstruction of 20 heart phases, 4.1 ms echo time and 451
Hz/pixel bandwidth. A GRAPPA technique (GRAPPA stands for
"generalized autocalibration partially parallel acquisition") with
a parallel acquisition factor of 2 was used to set the imaging time
per layer between 22 and 23 heartbeats, so that the measurements
could be undertaken while the breath was being held during
inspiration. If persons being examined were not capable of holding
their breath, the examination was undertaken with the patient
breathing freely and with multiple averaging, for example with
triple averaging in order to reduce movement artifacts.
[0052] The computation of the velocity field from the
phase-contrast images and also the process visualization and the
analysis of the velocity field was able to be undertaken with known
software. Such software is described for example in the publication
Reiter G et al. "MR vector field measurement and visualization of
normal and pathological time-resolved three-dimensional
cardiovascular blood flow patterns" J Cardiovasc Magn Reson 2007;
9: 237-238.
[0053] Velocity vectors were shown as color-coded vectors
three-dimensionally in space. Length and color of the vector
represent the amount of the velocity, the direction of the vector
in the presentation of the direction of the velocity.
Three-dimensional velocity fields were projected with the aid of
velocity vectors onto a corresponding anatomical presentation. The
suppression of noisy pixels and a variable thinning of the vector
field allow an interpretation of the blood flow within the
anatomical context.
[0054] Different parameters were analyzed on the basis of the blood
flows determined. For example an analysis was undertaken of whether
an existence of vortexes in the main flow direction was present in
the main stem of the pulmonary artery, as is shown for example in
FIG. 2. If there was a vortex an analysis was undertaken of whether
concentric, ring or spiral-shaped curve movements in the blood flow
of the pulmonary artery were present, along which the velocity
vectors moved tangentially. In particular the relative period
t.sub.vortex, which specifies for how long such a vortex exists,
was determined. In this case the number of heart phases in which
such a vortex existed was divided by the total number of heart
phases in order to determine t.sub.vortex.
[0055] In such cases it was observed that a vortex formation of the
blood arose along the longitudinal axis of the pulmonary artery, if
a pulmonary hypertension under rest conditions existed in the
examined person. Persons without a pulmonary hypertension did not
exhibit any of these vortex formations.
[0056] For example an analysis was likewise conducted of whether in
the diastolic phase movement lines of the blood flow existed
upwards along the anterior wall of the main stem of the pulmonary
artery. Such behavior of the blood flow is typically shown in FIG.
1. It was consequently analyzed whether a blood flow along the
front wall of the pulmonary artery existed during the diastole
which does not exist on the posterior wall of the pulmonary artery
or existed to a lesser extent. As in the case of the detection of
vortexes, also in the case of the detection of such a flow behavior
the relative period t.sub.streamline can be determined during which
this flow behavior is present. The relative period t.sub.streamline
can be computed in a similar manner.
[0057] In such cases it has been shown that such flow behavior
correlates well with the presence of a stress-induced pulmonary
hypertension. Persons with a normal pulmonary blood pressure
exhibit neither a characteristic vortex formation nor a
characteristic asymmetric behavior in the blood flow of the
pulmonary artery during the diastole.
[0058] FIG. 3 shows the situation once again with reference to a
schematic overview with nine small schematic diagrams. The drawings
depicted show schematically typical striking features in the blood
flow for different respective basic diseases and for healthy
subjects.
[0059] The first, left column shows the typical flow behavior in
the blood flow of the pulmonary artery at three different points in
time in the heart cycle, for a person with a pulmonary hypertension
under rest conditions (PH at rest). The second, center column shows
the typical flow behavior, at the same point in time in the heart
cycle, for a person with a stress-induced pulmonary hypertension
(PH at stress" or PH during exercise). The third, right-hand column
shows the typical flow behavior, at the same point in time in the
heart cycle, for a person with a normal pulmonary blood pressure
(no PH).
[0060] During the systole at an early point in time at which the
blood flow increases (first, upper line, systolic acceleration
phase) the blood flow for the three types only differs slightly
(first line, left, center and right diagram).
[0061] During the systole at a later point in time, at which the
blood flow reduces (second, center line, systolic deceleration
phase), a person with a pulmonary hypertension at rest already
exhibits the beginnings of a vortex formation and uniquely
asymmetrical behavior in the blood flow of the pulmonary artery
with regard to the longitudinal axis of the pulmonary artery in the
anterior-posterior direction (second line, left-hand diagram).
[0062] At this point in time the blood flow in the pulmonary artery
for a person with a stress-induced pulmonary hypertension and for a
healthy person exhibits an asymmetrical flow behavior, but no
significant difference (second line, center and right-hand
diagram).
[0063] During the diastole--shown here during the mid diastole
(third, lower line)--the person with a pulmonary hypertension at
rest exhibits an asymmetrical flow behavior in the pulmonary artery
and a vortex formation (third line, left-hand diagram). The person
with a stress-induced pulmonary hypertension merely exhibits an
asymmetrical flow behavior without vortex formation (third line,
center diagram), whereas the person with a normal pulmonary blood
pressure does not exhibit this asymmetrical flow behavior (third
line, right-hand diagram).
[0064] FIG. 4 shows a diagram in which measured pulmonary arterial
blood pressures of different patients are plotted against the
relative time t.sub.vortex. A clear correlation between the
relative period and the measured pulmonary artery pressure can be
shown. A linear regression line can be described in this specific
case for example by the formula
MPAP(in mm Hg)=16.7+58.0.times.t.sub.vortex,
if t.sub.vortex, is determined as described above. The correlation
coefficient in this case amounts to 0.94.
[0065] From this type of correlation, which for example can be
stored in a processor unit, a predicted value for the mean
pulmonary arterial blood pressure can be obtained from the measured
flow behavior. Other variables which identify the pulmonary
arterial blood pressure, such as the systolic pulmonary arterial
blood pressure or the pulmonary vessel resistance can be predicted
in a similar way, possibly with a worse correlation. In this way it
is possible to quantitatively evaluate the blood flow in the
pulmonary artery and obtain medically informative results.
[0066] FIG. 5 shows a schematic diagram of the method steps
executed in the method. In a first step (step 31) measurement data
is recorded from which at least one part of the blood flow in the
pulmonary artery is able to be reconstructed at least
two-dimensionally in a plane which is essentially spanned by a
longitudinal axis of the pulmonary artery and by an
anterior-posterior direction. From the recorded measurement data
the part of the blood flow is able to be reconstructed at least at
a number of diastolic points in time in the course of a heart cycle
after a closure of the pulmonary valve. In particular the blood
flow is able to be reconstructed over the entire heart cycle.
[0067] In a further step (step 35) the measurement data is analyzed
as to at how many of the at least several diastolic points in time
in the flow behavior of the blood flow of the pulmonary artery an
asymmetry in relation to the longitudinal axis of the pulmonary
artery in the anterior-posterior direction is present. In
particular the measurement data can be analyzed as to whether and
for how long a vortex is present which has a vortex axis which lies
essentially transverse to the longitudinal axis of the pulmonary
artery and transverse to the anterior-posterior direction. Such a
vortex represents an especially strong form of asymmetry in
relation to the longitudinal axis of the pulmonary artery.
[0068] Advantageously before step 35 a reconstruction of the blood
flow can be undertaken from the measurement data and a graphic
presentation of the blood flow (step 33). Step 35 can subsequently
be performed on the graphic presentation of the blood flow.
[0069] For example algorithms can be implemented for evaluation
which evaluate the graphical presentation of the blood flow
automatically or semi-automatically in interaction with a user in
respect of the flow pattern sought. E.g. algorithms can be
implemented which evaluate the flow behavior in the blood flow and
detect vortexes with reference to their characteristic flow
behavior or recognize an asymmetry in the flow behavior in the
anterior third of the pulmonary artery by comparison with the
posterior third. A vortex could for example be detected by
analyzing whether self-contained lines are present along which the
velocity vectors are tangential to each other.
[0070] Depending on the implementation of the algorithm a user can
also mark specific areas according to which a characteristic blood
flow behavior is to be evaluated. This enables algorithms to be
implemented with less effort since less data must be evaluated. In
an especially simple variant a user can also be shown the different
images of a heart cycle, with a graphic presentation of the blood
flow for example via a monitor and a user can mark those images on
which a characteristic flow behavior has been detected earlier. A
processor unit can subsequently on the basis of these markings
determine the measure that characterizes how long the flow behavior
to be detected exists in the blood flow and thus for example
compute a predicted value for an average pulmonary arterial blood
pressure.
[0071] Depending on the implementation of the evaluation and the
analysis of the measurement data, a graphic presentation of the
blood flow is not absolutely necessary however. For example it is
also possible to compute flow values directly from the recorded
measurement data and evaluate them without a graphic
presentation.
[0072] In a further step (step 37) based on the analysis a measure
is determined which characterizes how long after the closure of the
pulmonary valve in the flow behavior of the blood flow of the
pulmonary artery the asymmetry in relation to the longitudinal axis
of the pulmonary artery in the anterior-posterior direction is
present.
[0073] On the basis of the measure for example, as explained above,
a predicted value for the mean pulmonary arterial blood pressure
can be created (step 39). On the basis of the measure however
information cam also be obtained as to whether a pulmonary
hypertension under rest conditions or a stress-induced pulmonary
hypertension have a specific probability of existing. As an
alternative or in addition a signal can be output as soon as a
measure exceeds a specific threshold value (step 41). This alerts a
user to the fact that possibly a pathological behavior is present
in relation to a pulmonary hypertension.
[0074] FIG. 6 shows a schematic diagram of the layout of a medical
imaging apparatus 51, on which such a method can be implemented or
executed. An imaging unit, for example a magnet 53 of a magnetic
resonance device with associated hardware components, can in a
known manner be employed for recording the measurement data. An
ultrasound device can alternatively also be used for example as an
imaging device or another imaging unit, with which data in relation
to the blood flow can be recorded in the pulmonary artery.
[0075] The medical imaging apparatus 51 in this case has a
processor unit 55, with which for example the imaging unit can be
appropriately controlled. The method can be implemented in this
processor unit 55.
[0076] This processor unit 55 in this case does not inevitably have
to be embodied as a single self-contained unit, as is shown in FIG.
6. The processor unit 55 can also be distributed between a number
of subunits and parts of the method can also be implemented on the
respective subunits. For example a subunit can control the imaging
unit while a further subunit of the processing unit is embodied
such that the measurement data to be recorded can be evaluated
automatically or in interaction with a user.
[0077] Although modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of his contribution
to the art.
* * * * *